1. Field of the Invention
The invention relates to a drive unit for automatically actuating a vehicle door, in particular the tailgate of a motor vehicle, it being possible to connect the drive unit to the vehicle door or to a transmission device by means of an output shaft, said transmission device executing a pivoting movement which corresponds to the pivoting movement of the vehicle door, and the drive unit comprising at least one first sensor device which can be connected to an electronic evaluation device and serves to detect the respective angular position of the vehicle door.
2. Description of the Related Art
One requirement of vehicle doors which can be automatically actuated is for the respective position of the vehicle door to be determined by means of one or more sensors since this information is needed, inter alia, for controlling the speed of the vehicle door and for disconnecting the vehicle door when it reaches an end position or for identifying an obstruction. For example, in a tailgate which can be automatically actuated, a lower speed is therefore required just before it reaches the upper and lower end positions, so that the tailgate is not driven against the end stops with its full weight. It is also important, when closing the vehicle door, to move said door slowly toward the door seal just before it is completely closed, in order to minimize the risk of the driver or passengers being injured.
The respective position of the vehicle door is usually determined by means of rotation angle detectors which are arranged, for example, on the output shaft of the drive unit or the hinge connection of the vehicle door. In order to detect the absolute value of the corresponding rotation angle of the output shaft, potentiometers or analog magnetic field sensors are predominantly used as rotation angle detectors.
Some disadvantages of the analog rotation angle detectors are that they are associated with relatively high costs, some parts exhibit a high degree of wear, and moreover they require a great deal of installation space.